Conventionally when natural mammalian tissue, such as blood vessels and bones must be replaced by synthetic materials, the synthetic material is put in place either with an adhesive or by suturing. There are many disadvantages with these practices. When a synthetic material is bonded to bone, for example, as is done in hip replacement, there is often failure of the adhesive bond. Synthetic materials sutured into place for purposes of replacing blood vessels tend to fail and leak at the suture. One reason for their failure is hyperplasia near the suture line. Thus causing the synthetic vessel to lose patency. Also thrombi tend to form at the surface lines, to come off, and to travel downstream thereby presenting a serious health hazard to the patient.
Moreover, at present there is no tubular material for blood vessel replacement that can be safely sutured in place as a means of replacing small diameter blood vessels, such as those found in the extremities of the body or in children. A small diameter (less than 6 mm) vessel replacement using presently available materials cannot be reliably implanted for a period of more than several months and expected to remain patent. Further, the period of time for which they remain patent diminishes as their diameter diminishes. This is thought to relate to the fact that gas nuclei are often trapped in the surface roughness of materials. As a result, the material activates the complement system of blood plasma and this enhances the adhesion and aggregation of both platelets and leukocytes and results in thrombus formation. As the diameter of the prosthesis diminishes, it is less and less tolerant of even any thrombus formation because of the danger of the prosthesis becoming occluded. It will also be appreciated that such adhesion could result in the formation of thrombi which can also be a serious health hazard to the patient.
Filling the inside volume of a tubular artificial vessel with saline is commonly done before the artificial artery is surgically placed in position. However, this does not remove the gas nuclei from the pores of the material, if the material has a low surface tension compared to the surface tension of the saline or phosphate solution. This situation would exist, for example, if expanded polytetrafluorethylene (PTFE) were exposed to an aqueous solution such as saline or phosphate buffer solution. When an artificial artery is prepared in this fashion for surgical implant, the gas nuclei give rise to the enhanced complement activation, cellular adhesion and thrombus formation referred to above.
In U.S. Pat. No. 4,164,524, a method and apparatus for treatment of the gas-permeable wall of certain types of medical tubing, which may be brought in contact with blood, is disclosed. This procedure removes the gas nuclei by contacting the synthetic material of the tubing with a blood-compatible solution on one side of the material and applying a vacuum to the other side of the synthetic material. However, this procedure cannot be used successfully to remove the air nuclei from certain materials that are otherwise potentially useful for artificial implants, such as arterial replacement. If this technique were to be applied to certain tubular materials suitable for replacement of arteries, such as expanded PTFE, the surface tension of the material would be considerably less than the surface tension of the saline priming solution. As a result, surface tension effects would prevent the priming solution from entering the pores of the material regardless of the extent of vacuum drawn. Thus, this method could not be used with advantage to prepare such a material for insertion into a blood vessel because it would not induce the priming fluid to enter the pores of the material. Immediately upon the vacuum being removed, the pores would refill with air and little advantage would have been gained from the priming procedure.